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  • Engineering General  (5)
  • Organic Chemistry
  • 1995-1999  (7)
  • 1
    Electronic Resource
    Electronic Resource
    A second order finite element method for the solution of the transonic Euler and Navier-Stokes equations (1995)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 20 (1995), S. 671-693 
    Details
    ISSN: 0271-2091
    Keywords: airfoil ; artificial viscosity ; upwinding ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The numerical solution of the compressible Euler and Navier-Stokes equations in primitive variables form requires the use of artificial viscosity or upwinding. Methods that are first-order-accurate are too dissipative and reduce the effective Reynolds number substantially unless a very fine grid is used. A first-order finite element method for the solution of the Euler and Navier-Stokes equations can be constructed by adding Laplacians of the primitive variables to the governing equations. Second-order schemes may require a fourth-order dissipation and higher-order elements. A finite element approach is proposed in which the fourth-order dissipation is recast as the difference of two Laplacian operators, allowing the use of bilinear elements. The Laplacians of the primitive variables of the first-order scheme are thus balanced by additional terms obtained from the governing equations themselves, tensor identities or other forms of nodal averaging. To demonstrate formally the accuracy of this scheme, an exact solution is introduced which satisfies the continuity equation identically and the momentum equations through forcing functions. The solutions of several transonic and supersonic inviscid and laminar viscous test cases are also presented and compared to other available numerical data.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650200802
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  • 2
    Electronic Resource
    Electronic Resource
    BOUNDARY CONDITIONS IN SHALLOW WATER MODELS - AN ALTERNATIVE IMPLEMENTATION FOR FINITE ELEMENT CODES (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 603-618 
    Details
    ISSN: 0271-2091
    Keywords: shallow water equations ; wave continuity equation ; boundary conditions ; finite elements ; generalized functions ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Finite element solution of the shallow water wave equations has found increasing use by researchers and practitioners in the modelling of oceans and coastal areas. Wave equation models, most of which use equal-orderC0 interpolants for both the velocity and the surface elevation, do not introduce spurious oscillation modes, hence avoiding the need for artificial or numerical damping. An important question for both primitive equation and wave equation models is the interpretation of boundary conditions. Analysis of the characteristics of the governing equations shows that for most geophysical flows a single condition at each boundary is sufficient, yet there is not a consensus in the literature as to what that boundary condition must be or how it should be implemented in a finite element code. Traditionally (partly because of limited data), surface elevation is specified at open ocean boundaries while the normal flux is specified as zero at land boundaries. In most finite element wave equation models both of these boundary conditions are implemented as essential conditions. Our recent work focuses on alternative ways to numerically implement normal flow boundary conditions with an eye towards improving the mass-conserving properties of wave equation models. A unique finite element formulation using generalized functions demonstrates that boundary conditions should be implemented by treating normal fluxes as natural conditions with the flux interpreted as external to the computational domain. Results from extensive numerical experiments show that the scheme does conserve mass for all parameter values. Furthermore, convergence studies demonstrate that the algorithm is consistent, as residual errors at the boundary diminish as the grid is refined.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    A DIRECTIONALLY ADAPTIVE METHODOLOGY USING AN EDGE-BASED ERROR ESTIMATE ON QUADRILATERAL GRIDS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 673-690 
    Details
    ISSN: 0271-2091
    Keywords: Euler equations ; directionally adaptive meshes ; edge-based error estimate ; structured grids ; mesh movement ; finite element method ; high-speed flows ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The present paper describes a directionally adaptive finite element method for high-speed flows, using an edge-based error estimate on quadrilateral grids. The error of the numerical solution is estimated through its second derivatives and the resulting Hessian tensor is used to define a Riemannian metric. An improved mesh movement strategy, based on a spring analogy, but with no orthogonality constraints, is introduced to equidistribute the lengths of the edges of the elements in the defined metric. The grid adaptation procedure is validated on an analytical test case and the efficiency of the overall methodology is investigated on supersonic and hypersonic benchmarks.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Extent of chiral inversion of the 2-arylpropionic acids by Cordyceps militaris (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 528-534 
    Details
    ISSN: 0899-0042
    Keywords: chiral inversion ; ibuprofen ; ketoprofen ; flurbiprofen ; indoprofen ; suprofen ; fenoprofen ; metabolism of 2-arylpropionic acids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fungus Cordyceps militaris has been previously shown to be capable of inverting the chirality of 2-phenylpropionic acid from its (R)-enantiomer to its (S)-antipode. The structure of this compound is similar to the 2-arylpropionic acid non-steroidal anti-inflammatory drugs, which have also been reported to undergo a similar chiral inversion process in mammals and man. We report here an investigation into the substrate specificity of the enzyme system present in C. militaris using pure enantiomers and racemates of ibuprofen and ketoprofen and racemates of indoprofen, suprofen, flurbiprofen, and fenoprofen and the structurally related compounds 2-phenylbutyric acid and 2-phenoxypropionic acid as substrates, using optimised incubation conditions developed for the inversion of 2-phenylpropionic acid. The results demonstrated that C. militaris is capable of inverting the chirality of all the compounds investigated, which suggests that the active sites of the enzymes are very flexible with regard to the molecular dimensions of the substrate molecule and the spatial occupation of the groups surrounding the chiral centre. Metabolism of all the substrates was observed but the rate of metabolism varied extensively depending on the substrate. Achiral HPLC analysis was used to detect any potential metabolites and the results suggested that the site of the metabolism appeared to be at the aliphatic side groups only, with the aromatic ring being left intact in all cases. These results suggest that C. militaris could be a valuable tool in the investigation of the prospective metabolic fates of new 2-arylpropionic acids during their development. Chirality 10:528-534, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    A mechanistic investigation of the microbial chiral inversion of 2-phenylpropionic acid by Verticillium lecanii (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 254-260 
    Details
    ISSN: 0899-0042
    Keywords: microbial chiral inversion ; 2-phenylpropionic acid ; kinetic isotope effect ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous investigations have described the development of nongrowing suspension of Verticillium lecanii as a microbial model of the mammalian chiral inversion of the 2-arylpropionic acids (2-APAs). Mechanistic studies in mammals have shown that inversion involves loss of the α-methine proton but retention of the original atoms at the β-methyl position, and a mechanism has been proposed involving enzymatic epimerisation of acyl-CoA thioester derivatives of the substrate. Inversion of the 2-APAs by V. lecanii exhibits extensive intersubstrate variation in the presence, rate, extent, and direction of inversion, which are different from those observed in mammalian systems, possibly indicating differences in the mechanism of inversion between mammalian and microbial cells. This study involved the investigation of proton/deuterium exchange by 1H-nuclear magnetic resonance following incubation of deuterated derivatives of 2-phenylpropionic acid (2-PPA), a model compound, in cell suspensions of V. lecanii and incubation of undeuterated 2-PPA in cell suspensions containing D2O. The results indicated that the inversion of 2-PPA by V. lecanii also involved exchange of the α-methine proton but complete retention on the original atoms at the β-methyl position. No kinetic deuterium isotope effect was observed, indicating that loss of the α-methine proton is not the rate-limiting step of the inversion process. This suggests that the observed differences between microbial and mammalian systems probably involve the stereoselective acyl-CoA thioester formation step and not the subsequent epimerisation of the resultant diastereomers. Chirality 9:254-260, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    On the solution of block Hessenberg systems (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. 287-296 
    Details
    ISSN: 1070-5325
    Keywords: block Hessenberg matrix ; block Toeplitz matrix ; linear system ; queue ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This paper describes a divide-and-conquer strategy for solving block Hessenberg systems. For dense matrices the method is as efficient as Gaussian elimination; however, because it works almost entirely with the original blocks, it is much more efficient for sparse matrices or matrices whose blocks can be generated on the fly. For Toeplitz matrices, the algorithm can be combined with the fast Fourier transform.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nla.1680020309
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  • 7
    Electronic Resource
    Electronic Resource
    NUMERICAL STUDY OF STEADY LAMINAR FLOW THROUGH TUBES WITH MULTIPLE CONSTRICTIONS USING CURVILINEAR CO-ORDINATES (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 1021-1041 
    Details
    ISSN: 0271-2091
    Keywords: curvilinear co-ordinate system ; constriction ; stenosis ; module ; finite volume ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The flow field through tubes with multiple axisymmetric constrictions in tubes was studied numerically. Two practical problem cases were considered and the numerical scheme was developed for both. In the first case there are one, two, three and four constrictions in the tube. The effects of the number of constrictions on wall shear stress, pressure drop, streamline, vorticity and velocity distributions as the flow passes through the tube were studied and the development of the periodicity characteristics was investigated. In the second case there were multiple constrictions in the tube equidistant from each other. For this case the governing equations were reformulated for a module at a sufficient distance downstream from the inlet where the entrance region effects could be ignored and flow field is assumed to repeat itself. The flow field solutions were obtained in this region. The governing equations were formulated in curvilinear co-ordinates and a finite volume discretization procedure was used to solve the problem. The computations were carried out over a range of Reynolds numbers between 50 to 250 for constrictions with 75 percent area reduction. The method is validated by comparing some of the solutions with experimental results.
    Additional Material: 19 Ill.
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